Typically tractors with a crawling device have a rear drive sprocket fitted to the frame to rotate about a first axis crosswise to the longitudinal axis and a front idler mechanism fitted to the carriage to rotate about a second axis parallel to the first axis. A track is looped about the drive sprocket and the front idler and meshes with the drive sprocket along a meshing arc, and a damping device for reducing vibration and noise produced by the moving vehicle. The damping device generally has a damping roller fitted to the drive sprocket and rotating about a third axis.
In a crawler traction device of the above type, the track normally comprises a chain of metal links, each of which comprises a shoe having grip ribs on the outside, and forks on the inside for hinging it to the adjacent links by transverse pins. In use, the teeth on the drive sprocket engage the link pins to produce the characteristic caterpillar movement of the track and so propel the vehicle.
Meshing of the drive sprocket with the links represents a major source of noise and vibration, on account of the drive sprocket—which rests on the ground, with the interposition of the track, along the portion of the meshing arc tangent to the ground—moving continually up and down, as it rotates, with respect to the track. In other words, whenever a tooth on the drive sprocket engages the gap between the pins connecting two adjacent links along the portion of the meshing arc tangent to the ground, the drive sprocket slumps sharply onto the track, thus producing noise and vibration.
The traction device as described in EP0810149B, attempts to solve this problem and is equipped with a damping device comprising a damping roller, which is coaxial with the drive sprocket and of such a diameter that its peripheral surface permanently contacts the inner surface of the shoes along the whole of the meshing arc, so as to form a gap, along the whole of the meshing arc, between the base surface of the drive sprocket and the track pins and so prevent the drive sprocket from impacting the pins.
In actual use, however, the above solution has serious drawbacks, due to the damping roller preventing the drive sprocket from meshing correctly with the track.